(1) Field of the Invention
The present invention relates to an optical head comprising a light emitting element such as a laser diode, for example, an optical head for reading data recorded on an optical recording medium such as a CD or a DVD and recording data on an optical recording medium.
(2) Description of Related Art
In recent years, information technology devices utilizing light emitting elements such as laser diodes have advanced remarkably. Such information technology devices include optical disk drives capable of recording data on an optical disk by laser light and reading the recorded data therefrom. An optical head is an extremely important component of such an optical disk drive, because its performance determines that of the optical disk drive. In order to realize high-speed recording and cost reduction of the optical disk drives, various attempts have been made. In the optical disk drive, the optical head records data by modulating laser light and applying the modulated laser light to an optical disk, detects return light from an optical disk to which laser light is applied and thereby converts data recorded on the optical disk into electrical signals.
An optical system of a conventional optical head is composed of a light emitting element (for example, a semiconductor laser diode), a light receiving element (for example, photodiode), an objective lens, a collimator lens, a diffraction grating, and so on. In the conventional optical head of such a structure, the following technique is typically employed (see Japanese Unexamined Patent Publication No. 10-177733). Only a lens holding means holding the objective lens is allowed to follow an optical disk, an emitted laser beam from the light emitting element is focused on a predetermined site of the recording surface of the optical disk, and the reflected beam from the recording surface is then guided to the light receiving element by the diffraction grating. However, this technique principally has the following two problems. The first problem is that the movement of the objective lens causes a difference between the principal ray of the emitted laser beam and the optical axis of the objective lens, leading to coma aberration. The second problem is that since the optical components are arranged separately into a component in the lens holding means that can follow the optical disk and components in a fixed part that does not follow the optical disk, the number of optical components increases, leading to difficulty in downsizing the optical head.
To cope with these problems, for example, there is suggested an optical head structure in which a an objective lens, a light emitting element and a light receiving element are mounted in the same housing and are made together movable in the focusing and tracking directions (see, for example, Japanese Unexamined Patent Publication No. 8-287499). Such an optical head in which a light emitting element and a light receiving element are mounted in the same housing and which has a mechanism that drives them together in the focusing and tracking directions is hereinafter referred to as an “optical-system-integrated optical head”. According to the structure of the optical-system-integrated optical head, the positional relationship among the objective lens, the light emitting element and the light receiving element does not change at all during tracking and focusing motions. This can prevent the above-mentioned coma aberration from occurring and reduce the number of optical components.
FIG. 9 is a cross-sectional view showing the structure of the conventional integrated (optical head. As shown in this figure, the conventional optical head 1000 comprises a lens holding means (housing) 1010, and the lens holding means 1010 and a heatsink (radiating plate) 1011 are integrally molded. Furthermore, the lens holding means 1010 is mounted internally with a light emitting element 1001, a light receiving element 1002, a diffraction grating 1003, a quarter-wave plate 1004, a reflecting mirror 1005, and an objective lens 1006. The light emitting element 1001 and the light receiving element 1002 are mounted on the heatsink 1011. The lens holding means 1010 is mounted externally with a movable-part-driving coil (magnetic circuit) 1007, which is fixed in an optical disk drive by an elastic supporting member (not shown). The movable-part-driving coil 1007 allows a slight movement of a moveable part which consists of the lens holding means 1010 and so on (hereinafter, referred to as an “actuator motion”).
An emitted laser beam from the light emitting element 1001 in the horizontal direction (the lateral direction in FIG. 9) passes through the diffraction grating 1003 and the quarter-wave plate 1004 and thereafter is reflected by the reflecting mirror 1005 in the generally vertical direction (the upright direction in FIG. 9). The emitted laser beam reflected by the reflecting mirror 1005 is focused on a predetermined site of an optical disk 1050. The focused emitted laser beam is reflected as a laser beam having an intensity distribution corresponding to recording/site information on the optical disk 1050. This reflected laser beam again passes through the objective lens 1006 and is then reflected by the reflecting mirror 1005. The laser beam reflected by the reflecting mirror 1005 passes through the quarter-wave plate 1004. Thereafter, it is diffracted and guided to the light receiving element 1002 by the diffraction grating 1003. The intensity distribution of the reflected laser beam is detected by the light receiving element 1002 and then converted into electrical signals by a photoelectric conversion device or the like. An arithmetic circuit (not shown) calculates a tracking error signal and a focus error signal based on these electrical signals. A predetermined power variation is applied to the movable-part-driving coil 1007 based on these error signals, thereby causing electromagnetic action. In this way, the lens holding means 1010 can be moved such that the emitted laser beam is always focused on a predetermined site of the optical disk 1050. Furthermore, the optical disk drive reads data recorded in the optical disk 1050 by detecting the intensity of the reflected laser beam from a predetermined site on the optical disk 1050. The intensity distribution is detected by the light receiving element 1002.
On the other hand, a large amount of Joule heat is produced during the actuation of the light emitting element 1001 and the light receiving element 1002. This Joule heat degrades the characteristics of the light emitting element 1001 and the light receiving element 1002 themselves. Therefore, in the optical head, a heat dissipating structure must be formed in the movable part to dissipate the produced heat. Thus, in the conventional optical-system-integrated optical head, the light emitting element 1001 and the light receiving element 1002 are mounted on the heatsink 1011 and a contact area between the heatsink 1011 and the atmosphere is increased. In this manner, heat generated in the light emitting element 1001 and the light receiving element 1002 is released into the atmosphere.